Appendix 2. Indicators for Analysis of
Water/Road Interactions
The following indicators may be useful in analyzing the effects of roads
on aquatic and riparian resources.
Exercise caution when any indicator. Indicators alone cannot answer
questions, and they can be misleading or misused. Indicators should
be chosen, applied, and interpreted only in the context of
understanding how roads can affect watershed processes. First,
processes must be understood, and then well thought-out hypotheses
formed about mechanisms of impact. Then, indicators and road
performance data can be developed to test the hypotheses and add
spatial and quantitative relevance. The results must then be
interpreted in the context of all other watershed processes, with a keen
eye to recognizing inherent limitations and assumptions.
Testing indicators
The use of an indicator implies the existence of certain environmental
conditions. Usually, this association is based on correlative studies
between some variable (the indicator) and the response variable of
interest. The true set of environmental variables that produce the
response are often complex, unmeasured, or unknown. The ability of
an indicator to correctly predict a response depends on the quality of
the correlative study and works best when applied under the exact set
of conditions under which it was developed. When an indicator is used
for a different purpose than intended, or subjected to a different set of
conditions, the results can be misleading or incorrect.
Before using an indicator or collection of indicators to draw
conclusions about the effects of roads on watersheds, the relation of
the indicator to actual effects should be tested. That is, actual data on
road performance should be related to the candidate indicator to
determine if it is sensitive to and can predict the effect of interest.
Simply because a good correlation is found between the indicator and
the observed effect does not imply that the measured indicator is the
causation of the effect; it may only be correlated to the response. For
example, there may be a good correlation between road density and
stream sediment levels. The causative mechanism is not the density of
roads, but the amount of compaction, drainage rerouting, unstable
fills, and other sources of erosion. Simply reducing road density
without paying close attention to reducing the sources of sediment will
not produce the expected result of reducing sediment. In the
discussion that follows, indicators testing is shown as an example of
this important step in using and interpreting indicators.
For each indicator, the following are given
• Name of indicator
• Questions potentially addressed
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Description of indicator
Units of indicator
Scales
Related indicators
Utility
Acquisition
-Data needs
Accuracy and precision
Durability
Monitoring value
Limitations
Typical availability
Where applicable
Examples
Development needs
Tools references
A note on the examples
For each of the indicators we provide examples from specific places
where they have been used in actual analytical efforts. Many of the
examples are from West Coast national forests, especially the Six
Rivers. These are given as examples only. Some of the example
indicators likely have general value while others might be of limited or
local value only. The examples and associated testing show relations
that should not be considered applicable to other geoclimatic settings.
Further development is needed
This appendix discusses a small set of relatively easy-to-derive
indicators applied to just a few areas. As analysts conduct roads
analysis, we expect that new ways to effectively and efficiently learn
about the influences of roads on watersheds will be discovered, and
indicators appropriate for specific areas will be developed.. We
encourage the active development and sharing of these approaches in
service of understanding road effects and putting them into proper
analytical contexts.
Acknowledgments
We acknowledge Stan Thiesen, Judy Wartella, and Van Hare for their
expert assistance to the Roads Analysis Team in preparing this
appendix.
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